1. Field of the Invention
This invention pertains generally to the field of aircraft display units.
2. Description of the Related Art
Airports employ lighting aids to assist the pilot when, for instance, approaching a runway to land. According to the Aeronautical Information Manual (“AIM”) published by the Federal Aviation Administration (“FAA”) of the United States (“US”), a Visual Approach Slope Indicator (“VASI”) may be comprised on either two, four, six, twelve, or sixteen light units referred to as near, middle, and far bars. Most VASI installations are consists of two bars—near and far bars—and may consist of two, four, or twelve light units. Some VASIs consist of three bars—near middle, and far bars—which provide an additional visual glide slope to accommodate high cockpit aircraft. This installation may consist of either six or sixteen light units. VASI installations consisting of two, four, or six light units are located on one side of the runway, usually the left. Where the installation consists of 12 or 16 light units, the units are located on both sides of the runway.
Referring to FIGS. 1A through 1C herein and as stated in the AIM, two-bar VASI installations provide one visual glide slope which is normally set at 3 degrees (FIG. 1A). Three-bar VASI installations provide two visual glide slopes (FIG. 1B). The lower glide slope is provided by the near and middle bars and is normally set at three degrees while the upper glide slope, provided by the middle and far bars, is normally one-quarter degree higher. This higher glide slope is intended for use only by high cockpit aircraft to provide efficient threshold crossing height. Although normal glide slope angles are three degrees, angles at some locations may be as high as four-and-a-half degrees to give proper obstacle clearance. Pilots of high-performance aircraft are cautioned that the use of VASI angles in excess of three-and-a-half degrees may cause an increase in runway length required for landing and rollout.
The basic principle of the VASI is that of color differentiation between red and white. Each light unit projects a beam of light having a white segment in the upper part of the beam and a red segment in the lower part. The light units are arranged so that the pilot using the VASIs during an approach will see the combination of lights as shown in FIGS. 1A through 1C.
The VASI is a system of lights so arranged to provide visual descent guidance information during the approach to a runway. These lights are visible from three to five miles during the day and up to twenty times or more at night. The visual glide slope of the VASI provides safe obstruction clearance within plus or minus ten degrees of the extended runway centerline and to four nautical miles from the runway threshold. Using a VASI, descent should not be initiated until the aircraft is visually aligned with the runway. Lateral course guidance is provided by the runway or runway lights. In certain circumstances, the safe obstruction clearance area may be reduced due to local limitations, or the VASI may be offset from the extended runway centerline.
Referring to FIG. 1D, a Precision Approach Path Indicator (“PAPI”) uses light units similar to the VASI but are installed in a single row of either two or four light units. These light are visible from about five miles during the day and up to twenty miles at night. The visual glide slope of the PAPI typically provides safe obstruction clearance within plus or minus ten degrees of the extended centerline and to 4 statute miles from the runway threshold. Using the PAPI, descent should not be initiated until the aircraft is visually aligned with the runway. The row of lights is normally installed on the left side of the runway and the path indications are shown in FIG. 1D. Lateral course guidance is provided by the runway or runway lights. In certain circumstances, the safe obstruction clearance area may be reduced due to local limitation, or the PAPI may be offset from the extended runway centerline.
Referring to FIG. 1E, tri-color visual approach slope indicators normally consist of a single light unit projecting a three-color visual approach path into the final approach area of the runway upon which the indicator is installed. The below glide slope indication is red, the above glide slope indication is amber, and the on glide slope indication is green. These types of indicators have a useful range of approximately one-half to one mile during the day and up to five miles at night depending upon the visibility conditions.
Referring to FIG. 1F, pulsating visual approach slope indicators normally consist of a single light unit projecting a two-color visual approach path into the final approach area of the runway upon which the indicator is installed. The on glide slope indication is a steady white light. The slightly below glide slope indication is a steady red light. If the aircraft descends further below the glide slope, the red light starts to pulsate. The above glide slope indication is a pulsating white light. The pulsating increases as the aircraft gets further above or below the desired glide slope. The useful range of the system is about four miles during the day and up to ten miles at night.
In U.S. Pat. No. 7,216,069 entitled “Simulated Visual Glideslope Indicator on Aircraft Display” and dated May 8, 2007, Hett discloses a simulated glide slope indicator displayed in familiar VASI symbology and comprised of an ideal glide slope target, and a variable-positioning pointer within a vertical deviation scale.
In U.S. Pat. No. 7,772,994 entitled “Aircraft Glide Slope Display System and Method” and dated Aug. 10, 2010, Gang He discloses a glide slope icon of a desired glide slope that is comprised of a stationary series of monochromatic geometric symbols. To display deviation therefrom, Gang He discloses a second indicator referred to as a glide slope deviation icon comprised of a variable-positioned series of polychromatic geometric symbols that are off and to the side of the pitch scale of an attitude indicator.